GB2198827A - Web temperature regulating apparatus - Google Patents

Description

1 - 4 2198827 TEMPERATURE REGULATING APPARATUS The present invention

relates to temperature regulating apparatus for regulating the temperature of a web of material, which is to be printed on, in a web drier during heating, especially a drier arranged 5 behind a rotary printing machine.

The drying of printing inks is very important, particularly in high-speed rotary printing machines, and can limit the running speed of the machines (depositing and smearing). In the case of heat influence on the freshly printed inks, the processes connected with the drying devolve more rapidly. Generally, hot air driers have gained acceptance. Drying by means of web driers, however, stresses the web to be printed on. Too high a temperature of the web causes shrinking and embrittlement, whereby difficulties may arise in further processing. The temperature of the web depends on the internal temperature of the web drier, the transit time of the web in the web drier, and a constant which is specific to the..,,eb material.

Web driers are known with a sensor which contactlessly measures the temperature of the web and wh.ich is a component of regulating equipment for regulation of the temperature of the web by means of setting the magnitude of heat supply to the web drier; compare, for example, the prospectus 'BUTAB - The new generation CLEAN AIR high speed hot a.ir drier', by BUTAB, Spanga, Sweden (published 1983).

Regulating equipment of this kind controls the heat supply in indirect dependence on the web speed and are appropriate for use during continuous printing. However, as long as the internal temperature of the web drier changes appreciably during heating-up of the drier and printing is not yet possible, a web which has already been 2 - drawn into the drier must be moved continuously and printers' waste ari ses. Minimisation of printers' waste requires the heating-up process to run down in the shortest possible time - i.e. full heat supply - and also movement of the web with the least possible speed. The regulating equipment of the above-mentioned kind does not solve this problem.

It would thus be desirable to so match the starting and speedingup of a rotary printing machine to the heating-up of a web drier that a minimum of printers' waste arises, in particular by bringing the temperature of a web of material, which is to be printed on, to the maximum permissible temperature value during the heating-up of the web drier and to keep it there.

According to the present invention there is provided temperature regulating apparatus for regulating the temperature of a web of material in printing equipment, the apparatus comprising a sensor e-ranced in a web drie- in the region of a web outlet thereof to sense the temperature of the web and to provide a signal indicative of the actual value of the sensed temperature, regulating means arranged to receive the sensor signal and to provide a regulating signal in dependence on deviation of the actual value from a predetermined fixed value, and setting drive means connected to receive the regulating signal and to control the setting of the web speed in dependence on the received signal.

Preferably, the fixed or target value is the maximum permissible Le.-,, pera'LUC-1 value TOr Lhe respective web of material to be printed on, the web speed being influenced in dependence on the regulating deviation.

M In a preferred embodiment the sensor for the measurement of the temperature of the web is arranged in the web drier near the web outlet, an actual value input of a regulator being connected to the output of the sensor and a target value input of the regulator being loadable by a predeterminable fixed value corresponding to the maximum permiss ible temperature value. The output of the regulator is connected with the input of a setting drive for the setting of the web speed.

To reduce the regulating deviation, the web speed is alterable in the same sense of effect as the alteration of the temperature of the web, i e. for example, an increase in the temperature of the web causes an increase in the web speed,. This makes it possible to control the web speed in indirect dependence on the course of the heating-up of the web drier. The web temperature in the web drier is continuously detected by the sensor and the signal of the temperature is constantly compared by the regulator with the signal of the target value of this temperature, i.e. the maximum permissible web temperature. In depend ence on the regulating deviation, the web speed is so influenced that an assimilatien the web temperature to the target value takes place.

Before the start of the heating-up of the web drier, the regulating equipment operates against a lower abutment, since the regulating deviation before the start of the heating-up according to amount and direction effects web standstill (zero speed) During heating-up of the web drier, the internal temperature of the drier approaches the final temperature value corresponding to the thermal equilibrium with a delay of first order. This temporal change in the internal temperature during the heating-up is a disturbance to which the regulating system reacts. At any time, the web 1,5 speed sets in, which is required for the assimilation of the web temperature to the target value, i.e. the maximum permissible web temperature. This means that the printing machine is speeded up in dependence on the course of the heating-up process of the web drier The speeding-up occurs with the minimum permissible web speed and printers' waste arises at the minimum rate.

An automatically or manually actuable change-over switch can be so arranged at the output of the sensor that the sensor is selectably either a measuring member of the regulating circuit for the regul- ation of the web temperature by means of the setting magnitude of weD speed or a measuring member of a regulating circuit for the regulation of the web temperature by means of the setting magnitude of heat supply to the web drier. This makes it possible, preferably taken into operation after termination of the heating-up, to regulate the internal temperature of the web drier or the web temperature in dependence on the web speed.

In another embodiment an anal og-to-di gital converter is inserted between the output of the sensor and the actual value input of the regulating means, the latter being a digital process computer. In that case, the automatic detection of the digitalised signal of the temperature to be regulated, the processing according to the transfer function of the regulating means and the output of the control signal for the control of the machine speed (web speed) can be carried out in real time operation by the process computer.

An embodiment of the present invention will now be more particular ly described by way of example with reference to the accompanying drawings, in which:

1 - 5 '- Fig. 1 is a block schematic diagram of apparatus embodying the invention; and Fig. 2 is a signal flow diagram for the apparatus of Fig. 1.

Referring now to the drawings, there is shown a sensor 2 for measuring the temperature V'B of a web of material 3 to be printed on, the sensor being arranged in a web drier 1 near the web outlet. The sensor can be, for example, a contactless measuring sensor sensitive to infrared radiation. An actual value input of a regulator 4 is selectably connected by way of a change-over swit"Ch 11 to the output of the sensor ? or to a regulating circuit 13 (see further below), and a target value input of the regulator 4 is loadable by a predeterminable fixed value corresponding to the maximum permissible temperature value. The output of the regulator 4 is connected with an input of a setting drive 5 for the setting of web speed v B 1 The regulator 4 is preferably a three-point regulator and the setting drive 5 preferably an I-member (electrically driven motor), advantageously forming an I-like two-run regulator with three discrete speeds (righthand running, standstill, lefthand running). Predeterminable response values of the three-point regulator 4 correspond to the tolerances of the predeterminable target value. The drive shaft of the setting drive 5 is connected to a transmitter 6 for the web speed, for example the shaft of a potentiometer, and the output of the transmitter 6 is connected to an input of drive control equipment 7. The regulating circuit 12 for the regulation of the web temperature by means of the setting magnitude of web speed is completed by a main drive 8, a gear transmission 9 and a main drive shaft 10.

For reduction of the regulating deviation, the web speed v B is alterable in the same effective sense as the alteration in the web - 6 temperature "B The web temperature in the drier 1 is constantly detected by the sensor 2 and a signal x m representing the web temperature is fed to the regulator 4. If the signal x m exceeds the upper or lower threshold value, then the setting drive 5 for the resetting of the transmitter 6 for the web speed is switched on in such a sense of rotation that an assimilation of the web temperature to the target value takes place through alteration in the web speed.

Before the start of the heating-up of the drier 1, the regulating equipment, consisting of the sensor 2, the regulator 4, the setting drive 5 and the transmitter 6 for the web speed, operates against a 'iovver abu'LITIEn-L. Th-js is the abutment of the transmitter 6 for zero web speed (machine standstill).

During heating-up of the drier 1, the internal temperature of the drier approaches the final temperature value with a delay of first order. This temporal change in the internal temperature is a disturb- ance to which the regulating system reacts.

At any time, the web speed v B sets in, which is required fnr i--".m:4,-n of the %,et temerature 'B to the target value,;,.--. the maximum permissible web temperature. This means that the printing machine is speeded up in dependence on the course of the heating-up process of the drier 1. The speeding-up occurs at the minimum permissible web speed.

Corresponding to the three-point behaviour of the regulator 4, the web temperature -01 B constantly pendulates about a single temperature value, which corresponds to the upper response value of the regulator 4, during the heating-up of the drier 1. This means that during the heating-uQ of the drier the two-run regulator 4 and 5 resets 7 - 1 1 X the machine speed only at two discrete speeds, either standstill or full rotational movement in a single direction. The turning on of damping medium, printing ink and printing is possible during the speeding-up.

For setting or correction of the continued printing conditions, the printer preferably utilises the time intervals of constant machine speed.

When the setting or the correction of these conditions have been completed by the printer, then the regulating circuit 12 for the regulation of the web temperature by means of the setting magnitude of web speed can be switched off and the regulating circuit 13 for the regulation of the web temperature by means of the setting magnitude of heat supply can be switched on through the automatically or manually actuable change-over switch 11.

The equipment for the regulation of the web temperature in the drier during heating-up can also be employed during the slowing-down of the printing machine, until at standstill. In this case, the web temperature l,B pendulates constantly about a single temperature value which-corresponds to the lower response value of the three-point regulator 4. The slowing-down also takes place with the minimum permissible web speed and has the advantage of complete utilisation of the heat energy stored in the drier after it has been switched off.

The maximum permissible web temperature is not a constant, but depends rather on the material of the web and on the printing inks. The response values of the regulator 4 are therefore settable.

Claims (4)

1 Temperature regulating apparatus for regulating the temperature of a web of material in printing equipment, the apparatus comprising a sensor arranged in a web drier in the region of a web outlet thereof to sense the temperature of the web and to provide a signal indicative of the actual value of the sensed temperature, regulating means arranged to receive the sensor signal and to provide a regulating signal in dependence on deviation of the actual value from a predeter mined fixed value, and setting drive means connected to receive the regulating signal and to control the setting of the web speed in deoendence on the received signal.

2. Apparatus as claimed in claim 1, comprising control means to control the temperature of the web by controlling supply of heat to the drier, and switch means to cause the sensor signal to be applied to a selectable one of the regulating means and the heat control means.

3. Apparatus as claimed in either claim 1 or claim 2, the regulating means comprising a digital computer connected to the sensor by way of an analog-to-digital converter.

4. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.

Published 1988 at T-ne Patent Office, State House, 66,71 High Holborn, Londin WCIR 4TP. Further copies may be obtained from The Patent Office, Sales Branch. St Mary Cray, Orpington, Kent BRS 3RD Printed by Multiplex techniques ltd. St Mary Cray. Kent. Con 1/87 3